1. Field of the Invention
The present invention relates to a liquid crystal panel and a liquid crystal projector, and particularly to the ones in which the liquid crystal panel is cooled by cooling liquid.
2. Description of the Related Art
A liquid crystal projector has been widely used as a projection type display apparatus having a large screen. As is known, a liquid crystal projector is an apparatus in which light emitted from a light source is made to enter a liquid crystal panel through an illumination optical system and light modulated in the liquid crystal panel according to an image signal is projected by a projection lens.
In order to obtain high luminance of the liquid crystal projector, there is a need for increasing the amount of light entering the liquid crystal panel by increasing the amount of light emitted from the light source, enhancing the efficiency in utilizing light in the illumination system and the like. However, when the amount of light entering the liquid crystal panel increases, temperature of the liquid crystal panel rises and therefore unfavorable effect may occur with respect to reliable operation of the liquid crystal projector. Accordingly, in order to suppress the rise in temperature of the liquid crystal panel, the liquid crystal panel needs to be cooled.
In the past, air from a fan is used to cool a liquid crystal panel in a liquid crystal projector as a method for cooling the liquid crystal panel.
However, these days, not only high luminance but also miniaturization and low noise are in demand with respect to a liquid crystal projector. Therefore, the above air-cooling method may have a disadvantage in light of design of a liquid crystal projector.
Specifically, since the air in a liquid crystal projector is warm in general, it is desirable to cool a liquid crystal panel by taking air from the outside of the liquid crystal projector, however, in order for air from the outside to be taken in, an opening through which the outside air is taken by a fan needs to be provided in a casing of the liquid crystal projector and also an air duct needs to be provided in the liquid crystal projector to lead the outside air into the liquid crystal panel. Further, a filter to remove dust from the air taken needs to be provided. Since comparatively large space is required for such an opening for taking air in, an air duct and a filter, miniaturization of the liquid crystal projector may be limited. Furthermore, there is also a limit in reducing noise caused by the fan.
As a cooling method to comply with the need for miniaturization and low noise, there is a method of cooling a liquid crystal panel with cooling liquid. As the liquid-cooled method, the following methods (1) and (2) have been proposed.
(1) A method in which the whole of the liquid crystal panel is immersed in liquid in a container
(2) A method in which a transparent sealed container having an input and output portion of cooling liquid is attached on the light source side (light entering side) of a liquid crystal panel and cooling liquid is circulated between the sealed container and a heat exchanger (refer to, for example, Published Japanese Patent Application No. H5-264947 (paragraphs No. 0010 to 0016 and FIG. 1))
However, in the liquid-cooled method (1), there is a possibility that the cooling liquid may exude into a liquid crystal material from a sealed portion where the liquid crystal material is sealed.
Further, in the above-described method (1), natural convection is caused in the cooling liquid due to the difference between temperature at a position close to the liquid crystal panel and temperature at a position other than that, and the natural convection is projected as a striped pattern on a screen.
Further, in the liquid-cooled method (2), since the side (light emitting side) opposite to the light source side of the liquid crystal panel is not cooled, the temperature rise of the liquid crystal panel may not sufficiently restrained.
Furthermore, in the liquid-cooled method (2), if bubbles are generated in the process of circulating the cooling liquid, the bubbles are projected as a dot pattern on the screen.
Moreover, in the liquid-cooled method (2), a load of the sealed container and piping is applied to the liquid crystal panel, which may cause registration (positioning of pictures of R (red), G (green) and B (blue)) to be displaced in a three-panel liquid crystal projector provided with three liquid crystal panels of R, G and B.
Therefore, it is desirable to obtain a technology in which the rise in temperature of a liquid crystal panel is sufficiently restrained by cooling the liquid crystal panel using cooling liquid and the exudation of the cooling liquid toward a liquid crystal material is prevented.